The invention relates to injection molding.
Injection molding is a technique in which objects may be formed by injecting a composition into a mold for the object. Injection molding can be used to form components for use in downhole applications in the oilfield industry, including components that contain metals. To form such metal-containing components using injection molding, a polymer is blended with a fine metal powder, and the mixture is processed by an injection molding apparatus. In some cases, a feedstock for an injection molding apparatus may be prepared by pelletizing a homogenous mixture of a powdered metal with a thermoplastic resin. Otherwise, an injection molding feedstock may be introduced directly into an injection molding apparatus. The non-metallic portion of the feedstock, generally an organic material such as a polymer, is referred to as the binder or the binder material.
After a part has been injection molded, it is usually conditioned to remove most of the binder material through a process called debinding. The binder can be removed with heat, a chemical solvent, or a combination of the two methods. While debinding typically does not cause a reduction in the size of a part formed by injection molding, debinding might generally cause a significant increase in the porosity of the part.
Injection molded parts are typically subjected to a sintering process where the part is heated to a temperature sufficient to cause the particles making up the part to fuse together. The sintering process usually causes the injection molded part to shrink, with a resulting increase in density and structural strength.
When powdered metallic mixtures are used for injection molding, the flow characteristics of the metal powder used may significantly impact the structural characteristics of the finished part once it has been debinded and sintered. One aspect of this relationship is that when the flow of the particles is hindered by interparticle friction during the metal injection molding process, it may result in an uneven distribution of particles in the finished part, thereby reducing the density and strength of the finished part.